A process for the production of semiconductor elements (semiconductor devices) includes various steps such as a lithography step, an etching step, and an ion implantation step. After completion of each step, and before moving to the next step, a cleaning treatment is carried out, which is intended to detach and remove extraneous material (fouling) such as the resist residue remaining on the substrate surface or other impurities, and to clean the substrate surface.
As a conventional cleaning treatment method, a process of detaching and cleaning a resist residue, fine particles, metal and naturally-oxidized films using a mixed solution of concentrated sulfuric acid and hydrogen peroxide (hereinafter, appropriately referred to as SPM), has been frequently used. In this method, the ability to detach extraneous material is excellent; however, since the oxidizing power of the treatment liquid is too strong, there have been occasions where gate insulating films composed of a high dielectric constant (high-k) material or the like, or substrates themselves are damaged during the treatment. Considering the current circumstances that miniaturization of semiconductor devices is in progress, such damage, even a partial one, may cause deterioration of electrical properties. Furthermore, since the dangerousness of the chemical itself, the incidents of rapid temperature rise, and the like have been raised as an issue with regard to the method of using the SPM, this method is not necessarily a satisfactory method from the viewpoint of operation safety.
Accordingly, there is a demand for a cleaning technology which has less influence on the gate insulating films, substrates and the like, and is superior in terms of safety. As an example thereof, a method of cleaning an ashing residue using an aqueous solution containing ammonium carbonate and having a pH value of equal to or greater than 7 and less than 8.6, in a carbon dioxide gas atmosphere, has been suggested (Japanese Patent No. 4017402).
On the other hand, in recent years, there is a tendency with regard to the ion implantation process, which is one of the production processes for semiconductor elements, that the amount of ion implantation is increasing. In that case, because the resist to which ions have been implanted is carbonized and crosslinked, and thereby the outermost surface is altered, it is known that complete detachment may be difficult depending on the chemical. While there is an increasing demand for imparting higher reliability to semiconductor devices, it is considered more difficult to meet a demand for an improvement in the cleanliness of the substrate surface. Therefore, development of a cleaning liquid for a more efficient removal of impurities, including ion-implanted resists and the like such as described above, is desired.
The inventors of the present invention conducted an investigation on the detachability of ion-implanted resists and the like such as described above, using the cleaning liquid used in the cleaning method described in Japanese Patent No. 4017402. However, the inventors could not obtain results that are entirely satisfactory, and now, new improvements are needed.